Generally, ballast refers to weight loaded on a vessel for the stabilization of the hull. A vessel is provided with a ballast system to minimize trim/heel phenomena and provide the vessel with stabilization such that the vessel does not overturn due to wind and wave actions. For example, a vessel such as a cargo vessel is provided with a ballast tank. The vessel arrives at a port for loading cargo in a state where the ballast tank is filled with seawater. Then, the vessel is loaded with cargo and leaves for a destination port after the seawater ballast has been discharged to the outside.
Solid powder or solid materials with high specific gravity are sometimes used as ballast, but water is generally used because water can be easily obtained near the vessel. Thus, most vessels include a ballast tank, i.e. a ballast system, which corresponds to a container containing seawater as a ballast material. Accordingly, vessels have also been equipped with pumps as a means for causing the container to be filled with seawater, and fluid devices such as pipelines for transferring the seawater to the container and valves for regulating the pipelines.
Meanwhile, mandatory rules for double-hulled vessels have been recently introduced due to serious marine pollution caused by the collision or stranding of vessels. Accordingly, a ballast tank is installed in a space between an outer shell and an inner shell defining a cargo bay.
Such a seawater ballast system for use in the conventional vessels needs to be further improved.
A vessel operates pumps and pipelines to contain ballast seawater in the vessel to a certain degree that the buoyancy influence on the entire hull can be canceled out. However, such a system has a problem that excessive working expenses due to frequent power loss, pump damage, the exchange of pipes and the like should be unnecessarily spent.
In addition, the seawater filled in the ballast tank of the vessel includes many microorganisms and is carried to the next port of discharge in such a state. To load cargo, the filled seawater is pumped out at the port of discharge. At this time, there is a problem that the microorganisms included in the seawater may cause serious changes in the ecological system of microorganisms living around the port of discharge. A variety of suggestions for solving the aforementioned problem have been provided, but they are relatively ineffective. Further, many countries have newly establish various kinds of regulations for solving the aforementioned problem.
The ballast tank is easily corroded on its surface exposed to the seawater filled therein, which may make the hull weaker. Due to this corrosion, the painting operation of the interior of the vessel and the exchange of steel plates of the vessel should be frequently performed, which may cause a great deal of repair and maintenance costs. Further, the seawater contaminated by the corrosion may have a serious negative influence on the marine environment.
In particular, it is very important that when the vessel is damaged, conventional methods cannot ensure the restoration and survival chance of the damaged vessels. For this reason, many mandatory regulations for the double-hull structure of vessels have been enforced. However, even in such a case, the restoration and survival chance of the vessel are very low, and thus, the resultant damage to the vessel is unimaginably serious.